The present invention relates to a process for producing directly reduced iron (DRI) or other mineral products by directly reducing materials containing iron oxides and/or other metal oxides in a rotary kiln using a solid carbonaceous reducing agent, such as coal, and, more particularly, to a method and means for injecting reducing agent into the discharge end of the kiln in an improved manner.
Many different methods have been suggested and used for carrying out the direct reduction of ores and other materials containing iron oxides and/or other metal oxides using solid carbonaceous materials, particularly coal, in a rotary kiln to produce directly reduced iron (DRI) and other mineral products. For example, in some of these processes the coal is fed into the kiln through the discharge end by mechanical or pneumatic means, such as respectively disclosed in U.S. Pat. No. 3,113,859 to Moklebust and U.S. Pat. Nos. 3,505,060 and 3,663,201 to Heitmann, and in some it is fed at the center of or along the kiln, such as disclosed in U.S. Pat. No. 3,206,299 to Senior et al. However, considerable problems have been encountered with these various approaches, many of which problems have been overcome by the process disclosed in U.S. Pat. No. 3,890,138 to Hockin. In this latter process a portion of the coal is injected or blown into the discharge end of the kiln, and the remaining portion of the coal is fed with the other charge materials at the charge feed end. The kiln is generally divided into a reducing zone toward the discharge end and a preheat zone toward the feed end, and the coal is distributed in the kiln in such a manner that the amount of coal injected from the discharge end is sufficient to aid in controlling the charge and gas temperature profiles throughout both zones of the kiln.
Although the process of Hockin was developed particularly for use in reducing ilmenite using high volatile coal, it has been found that the technique of feeding from both ends improves upon the other solid reducing agent feeding methods used in reducing iron-oxide-containing materials in rotary kilns to produce directly reduced iron (DRI) or when producing other mineral products with the direct reduction process. In co-pending U.S. application Ser. No. 266,602, assigned to the same assignee as the present application, the essential parameters appropriate for effective feeding through the discharge end are disclosed and the present invention improves upon the invention disclosed therein, particularly when the techniques are applied in a comparatively large kiln.